Unexpected lessons

Today, I was trying to teach my class some methods of descriptive writing, like using different verbs/adjectives, describing all their senses, etc. One thing I taught them was how to construct similes:

"... as __adjective__ as __ noun__ ..."

They caught on to the idea pretty quickly, so I just put up some adjectives on the board and asked them for nouns to fill in the second blank. We went through big, small, sweet, and then the last one I thought of was "stinky." I first had to explain that stinky meant something that smells bad, and then a couple girls said "rubbish" and "garbage," which are perfectly fine answers. One boy, however, looking up words on his cell phone's electronic dictionary, came up with "excrement." Trying to keep a straight face, I wrote it on the board and the following dialogue ensued:

Me: "_____, would you like to explain this word to to the class?"

Student: "Huh? Um...it is when you go to the washroom, and you have eaten something bad, and this is what comes out."

Class: *bursts into laughter*

Whatever works to get the point across...they will now never forget similes =P